Stable isotope tracers offer the possibility to specifically study the metabolic fate of meal fatty acids.Īlthough the data comparing the in vivo metabolism of saturated and mono- and polyunsaturated fatty acids are limited, there appears to be an acceptance that the majority of fatty acids, with the exception of stearic acid ( 22), are metabolized in a similar manner. Moreover, the differences in the abundance of fatty acids in specific blood lipid pools may in part be due to differences in the way that dietary fatty acids are handled, both in terms of absorption across the gastrointestinal tract and partitioning toward either esterification or oxidation. Surprisingly, there is limited evidence comparing the metabolic handling of the major dietary fatty acids in vivo in humans.
Once in the systemic circulation, they enter metabolic pathways or exchange with endogenous molecules, particularly phospholipids (PLs). When fatty acids are ingested, they are incorporated into chylomicrons within the enterocyte. The marked rapid incorporation of linoleate from a single meal into blood PL fractions may have functional consequences such as maintenance of membrane fluidity and may explain why linoleate is a useful biomarker of dietary intake. This pattern was also true for erythrocyte PL fatty acids. This was significantly greater than for oleate and palmitate (both 3 ± 0.3% P < 0.05). At 24 h, 10% of plasma PL-linoleate originated from the breakfast test meal. Using the values for isotopic enrichment in the different lipid fractions compared with the test meal, we calculated the contribution of meal fatty acids to the respective fractions. There was significantly more linoleate than the other two tracers in plasma cholesteryl ester and phospholipid (PL). both palmitate and linoleate for NEFA and VLDL-TG, respectively). This pattern remained in plasma nonesterified fatty acid (NEFA) and very low-density lipoprotein (VLDL)-TG ( P ≤ 0.01 and P ≤ 0.02 for oleate vs.
There was a tendency for differences in the concentrations of the tracers in plasma chylomicron-triacylglycerol (TG) (oleate > palmitate > linoleate). We traced the fate of fatty acids using equal amounts of linoleate, oleate, and palmitate given in a test breakfast meal in 12 healthy subjects.
We hypothesized that different classes of fatty acids would be variably partitioned in metabolic pathways and that this would become evident over 24 h. There has been much interest in the health effects of dietary fat, but few studies have comprehensively compared the acute metabolic fate of specific fatty acids in vivo.
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